1. Technical Field
The present invention relates to concrete forms in general, and to adjustable reusable devices for forming concrete stairs in particular.
2. Background Information
Concrete stairs are a desirable, durable, and relatively inexpensive option for providing pedestrian access between different elevations. As can be seen in FIG. 1, concrete stairways 12 typically include one or more steps 14, each having a riser 16 and a tread 18. The riser 16 extends from bottom end 20 to a top end 22 defining a rise 24. The riser 16 is arranged substantially parallel to, or slightly offset by an angle α (e.g., 1 to 5 degrees) from, a vertical plane (e.g., a y-z plane). A tread 18 may be described as extending from the top end 22 of the riser 16 to a distal end 26 (e.g., a bottom end 20 of a riser 16 in an adjacent step 14) defining a run 28. The tread 18 is arranged offset by an angle β from the riser 16 (e.g., 90°−α). In embodiments where the treads 18 are substantially parallel to the horizontal plane, the angles α and β are typically complementary.
One of the drawbacks to concrete stairways is that they are difficult to properly produce, particularly if the stairway is wide and has a large number of steps. The concrete is initially in a semi-liquid state and must be held in place by a form. If the stairway is large enough, the semi-liquid concrete will present a substantial load on the form, and will need to be vibrated during the forming process to ensure the concrete is properly settled. The vibration typically present an additional loading on the forms. As the concrete cures, the exposed surfaces of the concrete must be carefully finished to provide the desired surface texture. In many instances, concrete stairs produced on a build-site are custom formed from lumber, which forms are discarded after the single use. This manner of forming a concrete stair is consequently time-consuming, expensive, and has a substantial risk of error (e.g., forms not assembled correctly vis-à-vis dimensions, forms deflect/warp or break under load, etc. Currently available devices for forming stairs have not met commercial success. These devices often have limited configurability, or are difficult to use, or impede the user's ability to access the concrete during the pour and finishing thereafter, or some combination thereof.
What is needed is a device that can be used to form concrete stairs, one that is reusable, one that can handle the loads associated with large stairs, one that facilitates the pour and finishing of the stairs, and one that is easily configurable to handle a variety of different stair configurations.